[bluesaunders]

The gravatar is a nice touch, but it works even if my email is not signed up with your service, which felt a bit misleading.

I got the sense of, "this is the correct email address to login with because the system recognized me" when in fact it was the wrong email.

[simontabor]

Good point - the reason for it is we wanted it to be entirely independent of our users db for security/privacy reasons (and simplicity!)